1. Field of the Invention
The present invention relates to a process for destroying a rigid thermal insulator and more particularly such a rigid insulator installed around a pipe in a confined space, for example an oil well.
2. Description of Related Art
During the bringing in of an oil deposit, hydrocarbons flow in the pipe, known as the production string, from the bottom of the well to the surface. At the bottom of the well, the pressure and the temperature are relatively high, for example 100.degree. C. and 300 bar. As the hydrocarbons rise towards the surface, this pressure and this temperature decrease, with the result that the temperature at the outlet of the well is, for example, of the order of 30.degree. C.
This fall in temperature of the hydrocarbons in the production string has the effect of increasing the viscosity and the weight of these hydrocarbons, which can lead to a slowdown in their flow. Furthermore, the fall in temperature can sometimes cause the deposition, on the wall of the string, of paraffin hydrates or of liquid vesicles, for example water. If it accumulates in the pipe, this deposit can lead to serious operating problems, such as the slowdown of the hydrocarbons, indeed the complete blockage of the pipe. Generally, if it is desired to avoid these risks, the operator is obliged to treat this deposition phenomenon, either preventively, by injection of a chemical which inhibits the deposition, or curatively, by scraping or wiping the pipe with special equipment or alternatively by reheating it with an optionally available means. In all cases, these operations constitute a significant financial expenditure. This type of problem also exists in pipes which connect a wellhead to a distant processing centre.
The installation of thermal insulation around a production string or pipe, optionally coupled to an electrical heating system or other system, makes it possible to maintain the temperature of these flows during their journey at a high value, thus reducing depositions on the wall of the string and other problems associated with the temperature.
French Patent Application No. 9801009 discloses a process for the preparation of a mixture which can be injected and gelled in situ in a confined space, for example the annular space of an oil well, starting with a precursor to be gelled, which may or may not comprise solid particles, with a dilution solvent and with a gelling catalyst. This process comprises a first stage in which the dilution solvent and the gelling catalyst are mixed together and a second stage in which the resulting solution is mixed with the precursor to be gelled, the mixture thus obtained being injected into the confined space. According to the invention, each of the first or second stages is carried out in a static mixer. This process makes it possible, for example, to install an insulating jacket formed of organogel in situ in the annular space of an oil well.
The confined space can also comprise a thermal insulator composed of aerogel or xerogel powder synthesized ex situ and introduced into the confined space, for example by means of a metering screw for pulverulent products. It can also comprise aerogels synthesized in situ, as disclosed in the document FR 9513601.
Once a rigid insulating jacket has been positioned in the annular space of a well, it may happen that it is necessary either to modify the insulating characteristics of the jacket as a function of the change in conditions in the well or to carry out a maintenance operation on the well or to remove the production string from the well. The presence of a rigid insulating jacket in the annular space of the well makes this type of operation difficult, indeed even impossible.
In order to be able to carry out such operations on a well, it is necessary to remove the rigid insulating jacket beforehand.